A tremendous variety of devices used today rely on actuators of one sort or another to convert electrical energy to mechanical energy. The actuators “give life” to these products, putting them in motion. Conversely, many power (veneration applications operate by converting mechanical action into electrical energy. Employed to harvest mechanical energy in this fashion, the same type of actuator may be referred to as a generator. Likewise, when the structure is employed to convert physical stimulus such as vibration or pressure into an electrical signal for measurement purposes, it may be referred to as a transducer. Yet, the term “transducer” may be used to generically refer to any of the devices. By any name, a new class of components employing electroactive polymers can be configured to serve these functions.
Especially for actuator and generator applications, a number of design considerations favor the selection and use of advanced electroactive polymer technology based transducers. These considerations include potential force, power density, power conversion/consumption, size, weight, cost, response time, duty cycle, service requirements, environmental impact, etc. Electroactive Polymer Artificial Muscle (EPAM™) technology developed by SRI International and licensee Artificial Muscle, Inc., excels in each of these categories relative to other available technologies. In many applications, EPAM™ technology offers an ideal replacement for piezoelectric, shape-memory alloy (SMA) and electromagnetic devices such as motors and solenoids.
As an actuator, EPAM™ technology operates by application of a voltage across two thin elastic film electrodes separated by an elastic dielectric polymer. When a voltage difference is applied to the electrodes, the oppositely-charged members attract each other producing pressure upon the polymer therebetween. The pressure pulls the electrodes together, causing the dielectric polymer film to become thinner (the z-axis component shrinks) as it expands in the planar directions (the x and y axes of the polymer film grow). Another factor drives the thinning and expansion of the polymer film. The like (same) charge distributed across each elastic film electrode causes the conductive particles embedded within the film to repel one another expanding the elastic electrodes and dielectric attached polymer film.
Using this “shape-shifting” technology, Artificial Muscle, Inc. is developing a family of new solid-state devices for use in a wide variety of industrial, medical, consumer, and electronics applications. Current product architectures include: actuators, motors, transducers/sensors, pumps, and generators. Actuators are enabled by the action discussed above. Generators and sensors are enabled by virtue of changing capacitance upon physical deformation of the material.
Artificial Muscle, Inc. has introduced a number of fundamental “turnkey” type devices can be used as building blocks to replace existing devices. Each of the devices employs a support or frame structure to pre-strain the dielectric polymer. It has been observed that the pre-strain improves the dielectric strength of the polymer, thereby offering improvement for conversion between electrical and mechanical energy by allowing higher field potentials.
Of these actuators, “Spring Roll” type linear actuators are prepared by wrapping layers of EPAM™ material around a helical spring. The EPAM™ material is connected to caps/covers at the ends of the spring to secure its position. The body of the spring supports a radial or circumferential pre-strain on the EPAM™ while lengthwise compression of the spring, offers axial pre-strain. Voltage applied causes the film to squeeze down in thickness and relax lengthwise, allowing the spring (hence, the entire device) to expand. By forming electrodes to create two or more individually addressed sections around the circumference, electrically activating one such section causes the roll extend and the entire structure to bend away from that side.
Bending beam actuators are formed by affixing, one or more layers of stretched EPAM™ material along the surface of a beam. As voltage is applied, the EPAM™ material shrinks in thickness and growth in length. The growth in length along one side of the beam causes the beam to bend away from the activated layer(s).
Pairs of dielectric elastomer films (or complete actuator packages such as the aforementioned “spring rolls”) can be arranged in “push-pull” configurations. Switching voltage from one actuator to another shifts the position of the assembly back and forth. Activating opposite sides of the system makes the assembly rigid at a neutral point. So-configured, the actuators act like the opposing bicep and triceps muscles that control movements of the human arm. Whether the push-pull structure comprises film sections secured to a flat frame or one or more opposing spring rolls, etc, one EPAM™ structure can then be used as the biasing member for the other and vice versa.
Another class of devices situates one or more film sections in a closed linkage or spring-hinge frame structure. When a linkage frame is employed, a biasing spring will generally be employed to pre-strain the EPAM™ film. A spring-hinge structure may inherently include the requisite biasing. In any case, application of voltage will alter the frame or linkage configuration, thereby providing the mechanical output desired.
Diaphragm actuators are made by stretching EPAM™ film over an opening in a rigid frame. Known diaphragm actuator examples are biased (i.e., pushed in/out or up/down) directly by a spring, by an intermediate rod or plunger set between a spring and EPAM™, by resilient foam or air pressure. Biasing insures that the diaphragm will move in the direction of the bias upon electrode activation/thickness contraction rather than simply wrinkling. Diaphragm actuators can displace volume, making them suitable for use as pumps or loudspeakers, etc.
More complex actuators can also be constructed. “Inch-worm” and rotary output type devices provide examples. Further description and details regarding the above-referenced devices as well as others may be found in the following patents and/or patent application publications:    U.S. Pat. No. 6,812,624 Electroactive polymers    U.S. Pat. No. 6,809,462 Electroactive polymer sensors    U.S. Pat. No. 6,806,621 Electroactive polymer rotary motors    U.S. Pat. No. 6,781,284 Electroactive polymer transducers and actuators    U.S. Pat. No. 6,768,246 Biologically powered electroactive polymer generators    U.S. Pat. No. 6,707,236 Non-contact electroactive polymer electrodes    U.S. Pat. No. 6,664,718 Monolithic electroactive polymers    U.S. Pat. No. 6,628,040 Electroactive polymer thermal electric generators    U.S. Pat. No. 6,586,859 Electroactive polymer animated devices    U.S. Pat. No. 6,583,533 Electroactive polymer electrodes    U.S. Pat. No. 6,545,384 Electroactive polymer devices    U.S. Pat. No. 6,543,110 Electroactive polymer fabrication    U.S. Pat. No. 6,376,971 Electroactive polymer electrodes    U.S. Pat. No. 6,343,129 Elastomeric dielectric polymer film sonic actuator    20040217671 Rolled electroactive polymers    20040263028 Electroactive polymers    200402392807 Electroactive polymer transducers and actuators    20040217671 Rolled electroactive polymers    20040124738 Electroactive polymer thermal electric generators    20040046739 Pliable device navigation method and apparatus    20040008853 Electroactive polymer devices for moving fluid    20030214199 Electroactive polymer devices for controlling fluid flow    20030141787 Non-contact electroactive polymer electrodes    20030067245 Master/slave electroactive polymer systems    20030006669 Rolled electroactive polymers    20020185937 Electroactive polymer rotary motors    20020175598 Electroactive polymer rotary clutch motors    20020175594 Variable stiffness electroactive polymer systems    20020130673 Electroactive polymer sensors    20020050769 Electroactive polymer electrodes    20020008445 Energy efficient electroactive polymers and electroactive polymer devices    20020122561 Elastomeric dielectric polymer film sonic actuator    20010036790 Electroactive polymer animated devices    20010026165 Monolithic electroactive polymersEach of these publications is incorporated herein by reference in its entirety for the purpose of providing background and/or further detail regarding underlying technology and features as may be used in connection with or in combination with the aspects of present invention set forth herein.
While the devices described above provide highly functional examples of EPAM™ technology transducers, there continues to be an interest in developing more efficient EPAM™ transducers. The gains in efficiency offered by transducers according to the present invention may come in terms of preloading improvement, interface with driven/driving components, output, manufacturability, etc. Those with skill in the art will appreciate the applicable advantages.